Cardiac and cardiovascular diseases are very widespread in western industrial nations. By way of example, these days a quarter of German citizens suffer from high blood pressure and each year approximately 400 000 German citizens suffer a myocardial infarction or cerebrovascular accident, the main cause of which is arteriosclerosis. Arteriosclerosis is understood to be a disease of the arteries, in which, inter alia, calcium is deposited on the inner walls of the arteries. If the calcium seals off e.g. a coronary vessel, this can result in a myocardial infarction.
The so-called calcification score has been established for estimating the risk a patient has of suffering a myocardial infarction. By way of example, in order to establish the calcification score, image information relating to the heart in a patient is obtained by X-ray computed tomography and the calcification score for the patient is determined from the image information, i.e. the amount of coronary calcification in the region of the heart registered by the image information. According to Agatston's method, calcified regions in the image information are in the process initially marked by hand. A computer program then calculates the calcification score on the basis of the marked calcified regions.
The calcification score in humans with healthy coronary arteries varies with age and sex. Therefore, in order to be able to undertake an individual risk assessment, it is necessary to compare the measured calcification score to a comparison group of the same sex and the same age. This is carried out in the form of so-called percentiles. Low percentiles correspond to a low personal risk, high percentiles to a high risk. By way of example, a calcification score below the 10th percentile means that less than 10% in the comparison group have a lower calcification score; the risk of a myocardial infarction thus is low.
The classification of a patient's risk can for example be carried out on the basis of a table. Hereinbelow, such a table is indicated in merely an example fashion:
Coronary calcificationAssessment of thescore (Agatston)coronary sclerosisRisk assessment0-10None/minimalLow risk11-100ModerateModerate risk101-400 SignificantIncreased risk401-1000PronouncedHigh risk
Someone is considered a risk patient if their value lies above the 75th percentile, corrected for age and sex. It thus is a relative value compared to that of an overall population. In the case of unfavorable values, cardiologists suggest a significant decrease in low density lipoproteins (LDL) because a high calcification score is connected with a medium to high risk of developing cardiovascular disease within the next 2 to 5 years.
The calcification score is generally obtained on the basis of a cardiac scan using X-ray computed tomography, during which no contrast agent is administered to the patient. Thus it is difficult in anatomical terms to assign the determined coronary calcification to the coronary vessels because the coronary vessels lack contrast in the image information. Thus, the calcification score merely specifies how much coronary calcification is present in the coronary vessels, but does not differentiate the number of the four main coronary vessels in which the coronary calcification was measured.
Although this information could be obtained using so-called coronary CT angiography, it cannot be used per se for determining the calcification score because a contrast agent has to be administered to the patient and the work has to be undertaken at a higher radiation dose. Whereas the radiation dose for a CT scan for determining the calcification score is approximately 0.8 mSv, the radiation dose in coronary CT angiography lies between approximately 4 and 20 mSv.
However, the differentiation according to the number of coronary vessels in which the calcification score was measured or how the coronary calcification is distributed over the coronary vessels has a decisive influence on assessing the risk for the patient. If the assumption is made that the calcification score recorded by X-ray computed tomography is constant, it immediately becomes apparent that the concentration of this calcification volume in only one coronary vessel has much more drastic effects on the blood supply of the heart than a more even distribution of the coronary calcification to all four coronary vessels.